The present invention is in the field of ceramics and ceramic composites.
This invention relates to methods and apparatus useful in the ceramics industry. More specifically, this invention relates to the fabrication of high melting, wear-resistant ceramics and ceramic composites at low temperatures.
Ceramic-rich composites have many potential applications, such as in rocket nozzels, high-temperature valves, wear-resistant mining parts, and automotive brakes. These ceramic-rich composites provide the valuable properties of having a high melting temperature, necessary in these potentially heat-intensive applications, and being wear and creep resistant, as many of these applications involve grinding or repetitive wear conditions. The use of these materials has been hampered by the inability to produce low-cost composites that are capable of retaining both a high strength and a high toughness. One major obstacle to producing such low-cost ceramics and ceramic composites is the need to form the materials at a high temperature, which greatly increases the overall cost of the materials. It is desirable to obtain an economical method for producing such materials.
It is therefore an object of the present invention to develop a method for fabricating high melting, wear-resistant ceramics or ceramic composites at relatively low temperatures.
Although described with respect to the field of ceramics and ceramic composites, it will be appreciated that similar advantages may obtain in other applications of the present invention. Such advantages may become apparent to one of ordinary skill in the art in light of the present disclosure or through practice of the invention.
The present invention includes ceramics and ceramic composites. This invention also includes machines or electronic apparatus using these aspects of the invention. The present invention may also be used to upgrade, repair or retrofit existing machines or electronic devices or instruments of these types, using methods and components used in the art. The present invention also includes methods and processes for fabricating such materials.
The present invention includes a method for producing ceramics and ceramic composites. The method comprises reacting (1) a fluid formed from melting a metal alloy, comprising at least one reactive metal and at least one non-reactive metal, and having a melting temperature below about 1500 C., with (2) a rigid, porous material (typically a ceramic, ceramic composite, or material otherwise capable of forming a ceramic upon reaction with the reactive metal(s)). The reaction should occur for a sufficient time at a temperature below about 1500 C., such that the fluid infiltrates the porous material and the active metal(s) react(s) with the porous material so as to form a ceramic or ceramic composite having a melting temperature substantially higher than 1500 C.
The active metal(s) may be any metal(s) capable of forming a ceramic with the rigid, porous material, and is preferably selected from the group consisting of zirconium, titanium, hafnium and mixtures thereof. It is preferred that the non-reactive metal(s) does not participate in the formation of the ceramic phase of the product material, although some trace elements may remain in the material. It is also preferred that the non-reactive metal(s) be selected from the group consisting of copper, silver, iron, nickel, cobalt, zinc, cadmium, lead, bismuth, antimony, and mixtures thereof. It is preferred that the rigid, porous material comprise a material selected from the group consisting of borides, carbides, nitrides, carbon and boron. Carbon and boron are used in additive type reactions where the reactive metal(s) is/are added to form the ceramic. The rigid, porous material may also be preformed into a shape, the resultant ceramic or ceramic composite substantially maintaining that shape. As used herein, xe2x80x9cmaintainingxe2x80x9d a shape means keeping the same basic geometric shape, although there may or may not be some fluctuation in dimensions attendant to the reaction process.
It is preferred that the metal alloy have a melting temperature substantially below that of the product material, typically below about 1500 C., preferably below about 1300 C. It is also preferred that the reaction be carried out at a temperature substantially below that of the product material, typically below about 1500 C., preferably below about 1300 C. The resulting ceramic or composite may have a melting temperature of at least 2000 C., 2500 C. or even as high as at least 3000 C. It is preferred that the product material have a density relative to theoretical density substantially in excess of about 80%, or in excess of 90%. The non-reactive metal is preferably removed during the reaction as a liquid or gas. The metal may be removed by any appropriate process, such as extrusion, de-wetting, or vaporization.
The present invention includes another method for producing a material selected from the group consisting of ceramics and ceramic composites. In this method, a fluid formed from melting a metal alloy is reacted with a rigid, porous material. The metal alloy comprises at least one reactive metal and at least one non-reactive metal, and has a melting temperature as described above. The rigid, porous material comprises a ceramic bearing an element capable of being at least partially displaced by the active metal(s). The reaction should occur for sufficient time at a reaction temperature as described above, such that the liquid infiltrates the porous material and the reactive metal reacts with the porous material so as to form a ceramic or ceramic composite having a melting temperature in the ranges given above. The active and non-reactive metals used in this method are preferably those mentioned above. The rigid, porous material is preferably selected from the group consisting of borides, carbides, and nitrides. The porous material may be preformed into a shape that is maintained throughout the reaction.
The metal alloy preferably has a melting temperature below about 1300 C., and the reaction is preferably also carried out at a temperature below about 1300 C. It is preferred that the resultant ceramics and ceramic composites have a melting temperature of at least 2000 C., at least 2500 C., or even as high as at least 3000 C. It is preferred that the product material have a density relative to theoretical density substantially in excess of about 80%, and may reach as high as in excess of 90%. The non-reactive metal(s) is/are preferably removed during the reaction as a liquid or gas, by any appropriate means such as extrusion, de-wetting, or vaporization. Some small amounts of the non-reactive metal(s) may remain in the product material, i.e., typically less than 10 atom percent.
The present invention also includes a method using a low temperature reaction and infiltration yielding a high temperature ceramic/composite using a zirconium, hafnium or titanium/copper alloy and tungsten carbide, nitride, and/or boride System. The method involves reacting (1) a fluid formed from melting a metal alloy of copper and at least one active metal selected from the group consisting of zirconium, hafnium and titanium (such as zirconium copper), the metal alloy having a melting temperature as described above with respect to the general method, preferably below about 1500 C., with (2) a rigid, porous material comprising a ceramic selected from the group consisting of borides and carbides of tungsten, and mixtures thereof (such as tungsten carbide). The reaction should occur for sufficient time at a reaction temperature in the range described above, preferably about 1500 C., such that the liquid infiltrates the porous material and the active metal reacts with the porous material so as to form a ceramic or ceramic composite having a melting temperature substantially higher than 1500 C., or as otherwise described above with respect to the general method.
The porous material may be preformed into a shape, which shape being substantially maintained during the reaction. The metal alloy preferably has a melting temperature below about 1300 C., and the reaction is also preferably carried out at a temperature below about 1300 C. The resultant ceramic or ceramic composite preferably has a melting temperature of at least 2000C., at least 2500 C., or at least 3000 C. The copper may be removed during the reaction as a liquid or gas, by any appropriate process such as extrusion, de-wetting, or vaporization.
Also included in the present invention is a ceramic or ceramic composite produced by each combination and permutation of the above methods. Product materials made in accordance with the present invention have been found to exhibit good wear and creep resistance, spalling resistance, and temperature resistance, making them suitable for applications where these are advantages.